B What does plus/minus mean?

1. Feb 12, 2019 at 11:09 PM

Kendo

Not sure if this is the right "forum section" but what does "±" mean when it comes to writing a lab report? I don't remember this back in high school but idk.

2. Feb 12, 2019 at 11:56 PM

symbolipoint

That symbol means, "plus or minus".
Also it can be read, "The positive or the negative of...".

3. Feb 13, 2019 at 12:20 AM

Staff: Mentor

$y= \pm \sqrt{x}$ means, that both possible values are considered, e.g. in $x_{1,2} = -\dfrac{p}{2} \pm \sqrt{\left( \dfrac{p}{2} \right)^2-q}\,.$ So it's $x_1=-\dfrac{p}{2} - \sqrt{\left( \dfrac{p}{2} \right)^2-q}$ and $x_2=-\dfrac{p}{2} + \sqrt{\left( \dfrac{p}{2} \right)^2-q}\,.$

$G = (6.674 08 \pm 0.000 31) \cdot 10^{-11} \,\dfrac{m^3}{kg \cdot s^2}$ means, that the gravitational constant isn't known exactly but only up to a certain amount of significant digits. It is around $6.674 08 \cdot 10^{-11} \,\dfrac{m^3}{kg \cdot s^2}$ but possible values range between $6.673 77 \cdot 10^{-11} \,\dfrac{m^3}{kg \cdot s^2}$ and $6.674 39 \cdot 10^{-11} \,\dfrac{m^3}{kg \cdot s^2}\,.$ Of course there is only one exact value, but we currently cannot measure it better than within this range.

4. Feb 13, 2019 at 2:40 PM

davenn

WOW could you make it any more difficult ??
it was a B level question

Yes

so for example ....
I have a result of 50 ± 5 that is a result that is somewhere between 45 and 55 so the mid point is noted with the error margin
or I have a result of 100 ± 10% again the same thing but this time you are stating a percentage error margin

would be two easy examples of it's use

Dave

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